I purchased my new unlocked Samsung Galaxy S20 Ultra directly from the Samsung web page and activated it through Consumer Cellular (CC). CC uses T-Mobile and AT&T towers to service their customers in my area. All worked well including Wi-Fi Calling and even showed the Wi-Fi Calling shortcut in the pull-down menu when I activated CC service through the CC T-Mobile towers. Cellular service signal was very weak at home and a neighbor advised AT&T towers for better signal strength. So, at my request, CC mailed me a new Sim Card for CC service through AT&T towers. The cellular signal strength was actually a bit worse and Wi-Fi Calling was not available. But, thanks to Consumer Cellular's award winning customer service, a tech was able to talk me through manually adding code to the phone which enable Wi-Fi Calling while using the CC AT&T sim card. Unfortunately, no Wi-Fi Calling shortcut in the pull-down menu which is a huge issue if you actually use Wi-Fi Calling as I do at home due to poor cellular signal strength. CC reactivated my phone's account back to the original CC T-Moblie sim card they mailed me, I performed “Reset settings - Reset all settings to their defaults”, Powered Off the phone, replaced the CC AT&T sim card with the CC T-Mobile sim card and powered the phone on. I now have the Wi-Fi Calling shortcut in the pull-down menu along with Wi-Fi calling without having to enter any code to the phone settings. All is working well now with the Consumer Cellular T-Mobile sim card installed.